You'll face an interesting boss fight on this floor. Initially you'll square off against Dr.Lugae and Balnab. If you kill Dr.Lugae first, Balnab will explode and most likely kill a party member. If you instead kill Balnab, Dr.Lugae will take over and you will fight Balnab-Z... who will also explode and kill a party member. You can avoid this by killing both at approximately the same time. Regardless, the real fight is with the Lugaborg. He will use a Poison ability that seems to stifle your options in combat, but a concentrated assault will take him down. If you brought along a Bolt Claw for Yang, he can take advantage of the fact that Balnab and the Lugaborg are Mechs.
You'll have to return to the 5F and use the Tower Key to progress. You may want to stop at the save point, since the Monsters haven't gotten any easier in the interim.
You'll have to return to the 5F and use the Tower Key to progress. You may want to stop at the save point, since the Monsters haven't gotten any easier in the interim.